Monolithic Instruments

Monolithic Instruments (New opportunities for wafer fabs) November 12, 2003 Jeremy Theil Agilent Technologies (jeremy_theil@agilent.com, tel: 408 553-4495)

Outline Trend in Manufacturing and Instrumentation Definition of Monolithic Instruments Examples Elevated Photodiode Arrays OLED Microdisplays Digital Micromirrors Manufacturing/Integration Challenges Future Opportunities Page 2

Product Trends Instrumentation Reduced system size. Increased computational power. Increased operational speed. Improved levels of process control. Improved reliability of manufacturing systems. Reduced system cost. Integrated Circuits Reduced system size. Increased computational power. Increased operational speed. Reduced transducer size. Novel solid-state transducers/actuators. Reduced system cost. Largely Enabled by Integrated Circuits! Page 3

Semiconductor Manufacturing Current Manufacturing Tolerances Wafer flatness: < 100nm across a 300 mm wafer. Metal impurity concentration: < 1 x 10 10 cm -3. Stacking fault density: < 1/cm 2. Layer-to-layer alignment tolerance: < 25 nm. Linewidth control: 3 nm 3σ. Minimum feature half-pitch: 100 nm. Film thickness control: < 4% 3σ over 300 mm. Current typical high-volume CMOS device specs. Transistor Density: ~9 x 10 7 transistors/cm 2. Operating Frequency: ~1.7 GHz. Manufacturing Cost: ~ $32/cm 2. $3.6x10-7 /FET Page 4

Value of a Semiconductor Mfg. Platform Semiconductor Mfg Machining Mfg Mach./Semi. Minimum Feature Size 0.25 µm 100 µm 400:1 Alignment Tolerance < 25 nm ~ 10 µm 40,000:1 Manufacturing Cost $1 x 10-6 /FET ~$2 x 10-1 /switch 200,000:1 For the number of devices made, a semiconductor fab is the most precise and least expensive manufacturing environment. Page 5

Definition of Monolithic Instruments Monolithic instruments are miniaturized systems, combining conventional integrated circuits with novel solid-state components, that interact with their physical environment. Concept- Incorporate several instrumentation system functions onto a single die. Transducer/actuator Driver (analog function) Analog/Digital interface Signal processing Data analysis I/O Page 6

Classes of Monolithic Instruments Pre-integrated circuit. During integrated circuit fabrication. Post-integrated circuit fabrication. Adapted from: H. Balthes, and O. Brand, Proceedings of 14 th Eurosensors XIV, p1 (2000). Page 7

Monolithic Instrument Examples Some types of monolithic instruments that have been fabricated include: a-si:h photodiode arrays. Organic LED micro-arrays. Digital Micromirror Devices. Liquid-crystal microdisplays. Bio-assay array systems. Inter-cellular communications. Components proposed for future monolithic instruments include: Thin-film bulk acoustic resonators. Photonic crystals. Planar light-guide systems Group IV-based LEDs. SQUID magnetometers Page 8

Fabricated Monolithic Instruments Inkjet heads (Hewlett-Packard, Loveland and Corvallis). Digital micromirror displays (Texas Instruments). DNA microarray detectors (Infineon). Direct neuron communicators (Infineon). a-si:h photodiode arrays (Agilent). Organic LED microdisplays (Agilent, e-magin). a-si:h Photodiode Contact Interconnect Texas Instrument s DLP TI 2003 Neuron Communications Infineon 2003 Si Substrate a-si:h Photodiode array (Agilent Technologies) SXGA OLED microdisplay. Agilent Technologies Page 9

Advantages of Monolithic Instruments Better performance. Improved signal integrity. Access to novel transducer technology. Smaller. Cheaper. What we have come to expect from improvements in integrated circuit technology can be applied to instrumentation systems. Page 10

Monolithic Instrument Technologies Elevated Photodiode Arrays. OLED Microdisplays. Digital Micromirror Arrays. Page 11

a-si:h Elevated Photodiodes Hydrogenated amorphous silicon is a deposited semiconductor. Bandgap ~1.8 ev. Advantages Higher QE. Tunable spectral response. Lower thermal effects. Higher fill factor. Cheaper imager. Disadvantage Subject to metastabilities that can affect performance (Staebler_Wronski Effect). Page 12

Dielectric Isolation Interconnect Insulator Transparent Conductor p-type i-type n-type Top contact conductor Bottom Contact Two extra masking levels. Requires a dry etch with high selectivity between two conductive materials. Page 13

TFT-Based Monolithic Interconnections R. A. Street (ed.), Technology and Applications of Amorphous Silicon. Springer, p 162 (2000). Page 14

Local-via Monolithic Interconnect Structure Transparent Conductor p a-si:h i a-si:h Top Conductor Contact n a-si:h Bottom Contact IC Passivation US Patent 6018187 Page 15

Elevated a-si:h Photodiodes- Pixel Size Reduction a) c-si 3T Pixel a-si:h 3T Pixel Page 16

Integrated a-si:h Photodiode/CMOS Stack 0.35 µm 4LM CMOS process. 5.9 µm square pixel, on a 7 µm pitch. Interpixel isolation created by etching of the n-layer a-si:h. Planarized passivation layer. Passivation Photodiode Array Interconnect Pixel contact via Si substrate Page 17

a-si:h Material Properties g(e) (cm -3 ev -1 ) 5 10 16 4 10 16 3 10 16 2 10 16 1 10 16 Integrated DOS ~2.5-4 x 10 15 cm -3. Mid-gap peak ~ 0.88 ev from the conduction band edge. A second peak at ~ 0.83 ev. 1.85 ev band-gap. E a ~ 0.9 ev. E U ~ 56 mev. Deposition Rate > 30Å/s. 0 10 0 0.70 0.80 0.90 1.00 E c - E (ev) J. Theil, D. Lefforge, G. Kooi, M. Cao, G. Ray, 18 th ICAMS Proc., J. Non-crystalline Solids, in press, 2000. Page 18

Effect of p-layer thickness on quantum efficiency 1 0.8 Quantum Efficiency (el/ph) 0.6 0.4 0.2 200A p-layer 100A p-layer 0 400 450 500 550 600 650 700 Wavelength (nm) Page 19

Effect of layer doping on quantum efficiency 1 AA008 Spectral Response (Effect of B Doping) Quantum Efficiency (el/ph) 0.8 0.6 0.4 0.2 LD p Layer (08) Control (09) LDp LDn (12) No n-layer (20) 0 400 450 500 550 600 650 700 Wavelength (nm) Page 20

Dark Current Components Two components of dark current: Junction leakage. Array edge leakage. Guard ring prevents edge current from reaching the array. ι ito I I B I E I A x ι ring ι ctr Sweep guard ring and area diode together. Assume: Ix = 0. IE = IA A ring /A area diode. Page 21

Dark Current Density vs Electric Field Current Density (A/cm2) 1.E-08 1.E-09 1.E-10 1.E-11 9000A 7500A 5500A 4000A 3000A 1.E-12 0.0E+00 5.0E+04 1.0E+05 1.5E+05 2.0E+05 2.5E+05 Electric Field (V/cm) Page 22

Structures and Junction Parameters n-layer thickness: 500Å. ([P] 2 x 1020 cm-3) i-layer thickness: 3000 to 9000Å. (5500Å default value) p-layer thickness: 200Å. ([B] 7 x 1019 cm-3) Edge Intensive Diode Area Diode Guard ring Page 23

Effect of Pixel Edge Length on Reverse Bias Current (3000Å I-layer) 1.E-05 1.E-06 Current Density (A/cm2) 1.E-07 1.E-08 1.E-09 1.E-10 1.E-11 1.23E+06 microns 5.77E+05 microns 1.94E+05 microns 5.95E+04 microns 2.11E+04 microns 3.84E+03 microns 1.E-12 0 2 4 6 8 10 Voltage (V) Page 24

Stacked Elevated Photodiode Concept Page 25

Optical Response of Stacked Diode Elements 1 0.8 800A i 2000A i 9000A i 2000A i Filter 9000A i Quantum Efficiency (e-/ph) 0.6 0.4 0.2 0 400 450 500 550 600 650 700 Wavelength (nm) Page 26

a-si:h Color Sensor Image (640x480 4.9 x 4.9 µm pixel, 1900 lux) Page 27

OLED Microdisplays Organic Light-Emitting Devices (OLEDs) Charge transport mechanism: localized state-based hopping. Use for large area emissive displays, fabricated using evaporation or printing. Just gaining acceptance. Has lifetime issues. Applications Eyepiece imagers (digital cameras). Eyeglass displays. Computers Instrumentation Advantages over LCD microdisplays Smaller Brighter (more power efficient). Less expensive (fewer components required). Thanks to Howard Abraham for driving the Ft.Collins Development Page 28

Microdisplay Systems LCD/LED-based Microdisplays Microdisplay Based on Light Emitting Polymers LEP CMOS Silicon APIX Value Proposition: Simpler, Cheaper, Brighter Page 29

Organic LED Materials Organic LED s: Materials and Devices Low work function cathode (Ca, Mg, Li/Al) V High work function anode (ITO, Au, Pt) Light Glass Electron Transport Emission Layer Hole Transport Layer OLEDs rely on organic materials (polymers and small molecules) that give off light when tweaked with an electrical current Small Molecules (vacuum evaporated) HTL: metal-phthalocyanines, arylamines (CuPc, NPD) ETL, EML: metal chelates, distyrylbenzenes Eastman Kodak, Pioneer, Idemitsu Kosan, Sanyo, FED Corp., TDK Polymers (spin cast) HTL: conducing polymers (PDOT, PANI) ETL, EML: polyphenylenevinylenes, fluorenes CDT, Philips, Uniax, Dow Chemical, DuPont N N N N O Al O O N R 1 R 1 n R 1 R 1 n NPD (HTL) Alq 3 (ETL, EML) R-PPV (EML) Polyfluorene (EML) Operating voltage ~10V Operating voltage ~5V Page 30

Organic Electroluminescence Organic electroluminescence by charge injection + Anode (ITO) (~ 4.8-5.1 ev) LU MO HOM O HTL DE A + + + + + + DI P CDT: http://www.cdtltd.co.uk LUMO HOMO ETL, EML Polymer OLED - Cathode (Ca, Mg) (~ 2.9-3.7 ev) Luminescence intensity (arb. units) 1.0 0.8 0.6 0.4 0.2 0.0 400 500 600 700 Wavelength (nm) Hole injection from high work function transparent anode (ITO) and transport through HTL Electron injection from low work function cathode (Ca, Mg, LiF/Al, CsF/Al) and transport through ETL Since I P < E A electrons are blocked by HTL and holes tunnel to ETL Formation of excitons and light emission from ETL Diode-like I-V (no light on reverse bias) Low turn-on voltage ( ~ 2 V) Operating voltage >> turn-on voltage Charge Injection limitations Charge Transport limitations Efficiency 1-5% ph/el 1-22 lm/w NP D/Alq 3 125 nm EL PL Page 31

OLED Diode Construction Process Overview for APIX/LEP Microdisplay Device Layout: Emitted Light Seal Layer (Transparent) Cathode (Semitransparent) Light Emitting P olymer (Diode) Electrical Schematic Light Emitting Polymer (Diode) ANODE ANODE ANODE APIX Active Ma trix Circuit on Silicon Page 32

OLED Challenges Environmental sensitivity. Device lifetime. Page 33

OLED Diode Structure Process Overview for APIX/LEP Microdisplay Device Layout: Specific Fabrication Steps (sequence is bottom up): Transparent Passivation Layer 2 Transparent Passivation Layer 1 Semitransparent Cathode Layer 1 Semitransparent Cathode Layer 2 ANODE P olymer Layer (ETL, EML) P EDOT Layer (HTL) ANODE APIX Active Matrix Circuit on Silicon ANODE Functional test, Mount chips to daughter board, Wire bond pads to board, Final test Encapsulate cathode with seal process steps. N2 atmosphere. Thermally evaporate semitransparent cathode using diesized shadow mask. N 2 atmosphere. Spin Electron Transport Layer (also the Emission Layer) light emitting polymer. N 2 atmosphere. Bake PEDOT (180ºC, 1 hr). Spin Hole Transport Layer (PEDOT). Surface clean (IPA/O 2 Plasma). Final metallization optimized for anode and bonding pads. Anodes form reflective pixels. Functional test. Process APIX on 6 or 8 silicon wafers. Page 34

OLED Microdisplay Driver Circuits Pulse-width modulation pixel driver circuit. Page 35

OLED Microdisplay Operation MGM MGM Page 36

Digital Micromirrors Invented at Texas Instruments in 1987 (by Larry Hornbeck). Build hinged mirrors from BEOL metallization over SRAM pixels. Operates by electrostatic attraction between mirror and pixel electrodes. Page 37

Digital Micromirror- Construction Texas Instruments Page 38

Digital Micromirror- Schematic Texas Instruments Page 39

Digital Micromirror- Mechanics Texas Instruments Page 40

Digital Micromirror- Applications Projections Displays Digital Movie Projectors Digital Printing and Photofinishing 3D Non-holographic displays Maskless photolithography DNA sequencing Broadband switching Holographic storage Anywhere LCD can be used, with higher contrast. http://www.dlp.com/dlp_technology/images/dynamic/white_papers/152_newapps_paper_copyright.pdf Page 41

Integration Challenges Known Issues Material compatibility with the nominal process flow. Adverse effects of the standard structures. Adverse effects of the new structures. Manufacturability of new unit modules. Materials optimization. Material performance considerations. Integration compatibility considerations. Unknown Issues There will be plenty of them. We encountered 8 major issues in one project. Example: The 9 causes of adhesion failure. Expect the unknown! Page 42

The Future Integrated circuit manufacturing platforms can be extended to make monolithic instruments. Many classes of monolithic instruments can be created. The attributes of monolithic instruments enable hundreds of new applications. Low cost Small size There are plenty of opportunities out there. Who is going to take advantage of them? Page 43